Tunable resonant circuit



Jan. 16, 1951 GQDBEY 2,537,985

TUNABLE RESONANT CIRCUIT Filed Sept. 21, 1945 Qwuwbov JOSIAH J. GODBEY wNM W Patented Jan. 16, 1951 UNITED STATES PATENT OFFICE TUNABLE RESONANT. CIRCUIT Josiah J. Godbey, United States Navy Application September 211;,1945..Serial-No;617,896

2 Claims. (01. 1:78-44); (Granted. under. the act of March 3, 1883; as.

amended April- 30, 1928; 370 0. G.. 757) This: invention relates to shorting devices for A tuned transmission lines, and more particularly to an adjustableshorting device for a pair of transmission lines;.. r

In certain types of high-frequency electronic 1' apparatus, it-is a practice to employ tuned transmission on lines as resonant circuits. For example, certain high-frequency oscilator circuits employ transmission lines todetermine frequency of'oscillation. In such cases, it may become dcsirable to. provide some-means for adjusting the resonant frequency of the transmission line. Heretofo-re, one method of accomplishing this hasbeen to employashorting bar which extends between the transmission lines, and the ends of the bar are connected thereto, the shorting bar being moved longitudinally with respect to the transmission line by a rotatable lead screw. .At ultra-high-frequencies, however, the lead screw introduces undesirable capacitive effects and in any event, it is difiicult to provide a good electrical contact between the ends of the shorting bar and the transmission lines.

In accordance with one embodiment of this invention, an adjustable shorting device may be provided for shorting a pair of spaced, parallel transmission lines, comprising a pair of spaced, coaxially disposed, externally threaded discs, the peripheries of which engage the opposed, inner sides of the transmission lines, which are suitably threaded. A spring is mounted between the discs to urge them apart to cause their peripheries to engage tightly the threaded portions of the transmission lines while keying means are provided to cause the discs to rotate together as the position of the shorting device is adjusted longitudinally with respect to the transmission line.

Other objects and advantages of the present invention will be apparent from the following detailed description taken in conjunction with the drawings, wherein:

Fig. 1 is a plan view of a pair of spaced, parallel transmission lines having associated therewith a shorting device constructed in accordance with one embodiment of this invention;

Fig 2 is an end view of the structure shown in Fig. 1 and Fig; 3 is an enlarged, longitudinal vertical view of a portion of Fig. 1.

Referring now to the drawings, it will be seen that a pair of spaced, parallel transmission lines 5 have been provided, having a circular plate 6 mounted across the left end thereof, as viewed in Fig. 1,' and being rigidly secured thereto serves to maintain the proper spacing between the left tweenth'e discs 1 and 8 and, the left end of the q portions of; the. transmission lines; The right ends'of the transmission lines may be connected to: asuitable electronic device (not shown),ias is' well known. in the art. The resonant frequency of these transmission lines, and as theelectrical length is' decreased, the frequency at which the lines will be resonant; is correspondingly increased.

In order to providea simple and efficient shorting device whereby the electrical length of the transmission lines may be readily varied, in accordance withthe-present invention a pair," of spaced, coaxially disposed-substantially parallel, externallyrthreaded' discs"! and 8 are locatedzbee tween the transmission lines 5, the inner opposed 'sides'of the transmission lines 5 being suitably threaded'to receive and engage the threadedperipheries of the discs I and 8. Thus by rotating the discs 1 and 8 to cause them to travel to the right or to the left, as viewed in Fig. l, the electrical length of the transmission line may be decreased or increased. Rotation of the discs is efiected by inserting a screw driver, or other suitable device through an aperture 9 formed in the central portion of the mounting plate 5 and engaging the end thereof with a transversely extending slot I0, formed in the left face of the disc I, as viewed in Figs. 1 and 3. In order to cause the disc 8 to rotate with the disc I, a pair of keying or guide pins I I are mounted on, or integrally formed with, the right side of the disc I and extend to the right therefrom into suitable apertures l2 formed in the left face of the disc 8. In assembling this shorting device on the transmission line 5, it will be understood that the desired spacing between the discs 1 and 8 may be readily obtained. It is usually desirable that the spacing between the discs be held to a minimum. In order to assure a satisfactory electrical contact between the peripheries of the discs and the threaded sides of the transmission lines 5, and at. the same time to increase the frictional engagement therebetween to prevent the shorting discsfrom changing position after being adjustedya helically coiled spring 13 is located bespring [3 extends into a shallow recess M formed in the right face of the disc I while the right mission. line a screw driver is inserted through the aperture 9, and its end engaged with the slot In of the disc 1. The disc! is then rotated, thereby causing the disc 8 to rotate correspondingly and to move to the right or to the left, as viewed in Fig. 1, to decrease for increase the electrical length of the transmission line. The device of this invention, by reason of its compactness, provides a wider range of adjustment for a given size than is feasible with a shorting bar moved by a lead screw, and at the same time, by eliminating the need for a lead screw, eliminates the undesirable capacitive effects of the lead screw. Furthermore the need for providing spring contacts at the ends of the shorting bars, as is the conventional practice, is avoided by virtue of the engaging" pressure obtained by the use of the spacing spring'l3.

While this invention has" been described in conjunction with a pair of transmission lines, it will be understood that many other applications of this device are possible and that many changes and modifications may be made therein without departing from the spirit or scope of the present invention.

The invention shown and described herein may bemanufactured or used .by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

- What is claimed is:

1. A distributed constant radio frequency ad justably tuneable circuit comprising a two conductor open transmission line section having a pair of straight rigid conductor members, means for maintaining the members in parallel spaced relationship, complementary thread means on the 4 adjacent sides of the members, and flat annular externally threaded shorting means diametrically engaged by and between the members for thread-, wise adjustable positioning along the line sec tion.

2. A distributed constant radio frequency adjustably tuneable circuit comprising a two conductor open transmission line section having a pair of straight rigid conductor members, means for maintaining the members in parallel spaced relationship, complementary thread means on the adjacent sides of the members, and shorting means comprising a pair of flat annular externally threaded discs diametrically engaged by and between the members for threadwise adjustable positioning along the line section, biasing means interposed between the discs for maintaining frictional engagement with the threaded members, and means for causing the discs to rotate together.

JOSIAH J. GODBEY.

CES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

